To meet the anticipated explosion of wireless demand by public mobile telephone users, it is necessary to use microcellular systems which have substantial capacity.
At the present time, Fixed Channel Allocation (FCA) is used to obtain access to the channels in the cells in substantially all systems deployed around the world. With FCA, a fixed set of channels are assigned to each cell. However, FCA is rigid and not adaptable to satisfying a volatile, shifting channel demand. As cellular and personal telecommunication networks evolve toward microcells, the channel demand profile can experience rapid changes. The rigid nature of FCA can be a serious obstacle to providing a communication channel to a mobile user at the time it is needed. In addition, centralized control of a cellular network system is subject to undesirable delays and vulnerable to disruptions.
With microcellular systems and increasing numbers of mobile users, current frequency planning and network control are rapidly becoming impractical and burdensome. One possible solution to the network management problems created by the use of microcells is Dynamic Channel Allocation (DCA) where each channel is available for use in every cell. DCA adapts to local interference and traffic conditions and removes the need for frequency planning. However, channel quality can be impaired by a channel in a nearby cell and/or a weak signal strength and, a channel quality level which is below threshold will prevent a channel from being immediately accessed by an incoming user.
To operate a network using DCA centrally, as it is envisioned, could result in the computer based switching system being overwhelmed. Specifically, the software manageability problem could be particularly acute. Moreover, for a centrally controlled DCA system, an elaborate network infrastructure for handling channel access information would be required. Additionally, reliance on central decisions tends to make a network vulnerable to failure and, at this time, there is a growing need for a reliable network. Furthermore, central control creates delays which are objectionable because timely channel access is critical.
Local autonomous control of channel access, where decisions are made by mobile telephones and/or bases rather than centrally, can result in most of the switching burden being removed and allow more handoffs to be accommodated faster. However, there are some very serious concerns about permitting local autonomy. One concern is that the algorithms may be unstable because uncoordinated users could work at counter-purposes to each other where each continually undermines what the other is attempting to achieve. A more serious concern is that during periods of peak demand, unstable cascades of reconfigurations of channel assignments can be inadvertently triggered which will take down the entire network when it is needed most. Even if local autonomous control would work, there is serious concern that there would be a serious performance penalty associated with using local instead of ideal central control.
Thus, local autonomously implemented DCA is an enticing concept, but is viewed as being potentially troublesome if not done correctly.
An improved distributed dynamic channel allocation method is required for use in microcellular communications which provides improved operation.